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In this comparison post, I will be looking at two species of Chorus Frogs that overlap in the eastern part of the Lone Star State. These two species are similar looking overall and although they probably aren't confused that often in the field, their calls are surprisingly similar.The Spring Peeper (Pseudacris crucifer) is a small "treefrog-like" chorus frog of the eastern United States. In many areas of the country it is the harbinger of spring as it starts calling very early in spring and its calls are so conspicuous around woodlands and even residential areas of the eastern US.

Spring Peeper (Pseudacris crucifer)Arkansas

The Spring Peeper gets it common name for its "peep"-like call. It get the species epithet crucifer from the x-shaped marking on its back (crucifer means cross-bearer). Otherwise Spring Peepers are light brown frogs with a few markings on their upper surface around the X and typically a dark mask that runs from the nose through the eye. A few Spring Peepers lack the back pattern but they usually have the dark mask.

Spring Peeper (Pseudacris crucifer)Arkansas

The Strecker's Chorus Frog (P. streckeri) is a similar sized chorus frog of the central US. It generally occurs in oak woodlands and into grassy savannahs. It will call from cultivated fields near woodlands as well. In Texas, this species occurs in the eastern half of the state but its populations east of the hill country appear to have decreased significantly in the last 50 years.Strecker's Chorus Frog is also a brownish frog with darker markings on the back. The back markings can be somewhat x-shaped similar to the Spring Peeper but they generally don't form a perfect x. They also have a dark mask like the Spring Peeper, but the mask of Strecker's Chorus Frog tends to be a bit more narrow.

Strecker's Chorus Frog (Pseudacris streckeri)DeWitt County, Texas

The Strecker's Chorus Frog is also a distinctly more stocky frog than the Peeper with a more massive body and stockier legs. It is also more terrestrial than the Spring Peeper. Spring Peepers often call from bushes and trees while the Strecker's Chorus Frog typically calls from the water or the ground near water.

Strecker's Chorus Frog (Pseudacris streckeri)Guadalupe County, Texas

The two species overlap over a large area of far east Texas, although the Spring Peeper is a much more common frog within the area of overlap. Strecker's Chorus Frog can be locally common but it is apparently absent from large parts of its former range. In the hill country it is still reasonably common along canyons and creeks.This map is adapted from the Herps of Texas website maps, although I have taken the liberty of filling in some counties where the species would be expected but haven't been recorded yet.

Even though Pseudacris crucifer is called the Spring Peeper, both of these species will call during the winter here in Texas as long as the temperatures are above freezing. Spring Peepers usually finish breeding in March in Texas, Strecker's Chorus Frogs will breed well into April and even May depending on rains.The two frogs are somewhat similar looking in general color pattern and overlap in at least certain parts of the state and they also both have a similar loud peeping call.The call of the Spring Peeper is a distinct, loud, whistled peep that carries a long distance.

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It's funny how you start a "project" without really knowing it is to become a "project". I had always been interested in herps (reptiles and amphibians) since I was a small boy and I had always been fascinated by the sounds of the outdoors. I did start reading about recording wildlife/natural sounds in the early 1980s, but never pursued it because recording gear was expensive and onerous to take in the field.Then in 2010 gear had not only come down in price (and my budget had increased since my undergrad days!), but it had become more field hardy and accessible. So I dove in and bought a microphone (Sennheiser ME66/K6 and an Olympus LS-10 recorder). I started off recording a few birds around my house then, since I'm a herp guy, expanded naturally to try a few frog calls.Once I got a few recordings of common species around me (Blanchard's Cricket Frogs, Gulf Coast Toads, Great Plains Narrow-mouthed Toads) and I began to get comfortable with the process of recording and editing recordings, I thought "I wonder if I can get all the species that occur in my area?". After a season of this with some success, I moved on to the idea of trying to get all the species that occur in my state.And so the project began. As I started collecting recordings from Texas, I had to opportunity to travel outside the boundaries of the state and the country so I took my recording gear with me....and my obsession began.So now my "goal" is to try and record as many species as I can. Yes there are good recordings of frog calls from many developed parts of the world, but they aren't always easy to access or can be expensive to buy. My goal was to provide a source of free recordings that people could use to help ID their frogs and toads. And mostly, I just enjoy doing it! 😁So here's my progress so far. I'm actually amazed I've managed to get this much stuff posted!

The White-lipped Frog (Leptodactylus fragilis) is a widespread frog from of the tropical lowlands from Southern Texas down into Panama and northern South America. Although it gets into Southern Texas, it is by no means common there and it may be one of the least often seen frogs in Texas.The difficulty of finding it in Texas is partly due to its limited range and period of activity, but also due to its habit of calling from partially flooded grassy areas where it may call from underneath clumps of grass or soil, or even from burrows underground. The frog photographed above was calling very loudly from an area of seemingly bare dirt with a few clumps of grass. I looked and looked and couldn't see it! Finally, I tracked it down to where it must be coming from and flipped a rock to find it calling from a burrow under the rock. Hopefully the females are better at tracking down males than I am! As a side note, I took this photo and took him back to the grass next to his rock. Within a few minutes, he had crawled back down his burrow and started calling again!The taxonomy of this frog species has been confused in the literature over the years. It has been listed as Leptodactylus albilabris (which is a different species that is restricted to Puerto Rico and the Virgin Islands) and Leptodactylus labialis which is not a valid name. Furthermore there is sometimes confusion in its relationship with the South American species, Leptodactylus mystaceus.Although it is called a "white-lipped" frog, many individuals I have seen didn't seem to have a very conspicuous white lip at all?

The call of the White-lipped Frog is a upward whistle "pru-uh" sound repeated many times in a row. The call starts off around 900Hz and slurs quickly up to around 1.6kHz.

This individual was recorded just south of the town of La Palmera, Alajuela, Costa Rica in August 2014. As is typical with calling Leptodactylus species, the frogs were never seen.
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White-lipped Frog Call from Costa RicaHere is a recording from south of the town of Pisté, Yucatan, Mexico. This recording includes the individual above that was calling from underneath the rock as well as a couple of others that were calling from burrows.
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White-lipped Frog Calls from Yucatan, Mexico.

OK, so this blog post is going to start off with a correction to a previous blog post. My previous blog post about the Cane Toad (Rhinella marina) discussed the Cane Toad as being a species native to Texas, Mexico, Central America, South America and introduced to a variety of places worldwide. But a recent study based on mtDNA and skull morphology has shown that this "species" is actually two species of toad! So I am changing my old blog record to cover Rhinella marina and will make a new post for the Texas species, Rhinella horribilis.The Giant Toad (Rhinella horribilis) is a massive toad occuring from South Texas down into Mexico, Central America and along the northwest coast of South America (west of the Andes).

Giant Toad (Rhinella horribilis)Costa Rica

In Texas, this species is restricted to the lower Rio Grande Valley, occurring along the river and inland from Laredo down to the mouth of the Rio Grande. In South Texas it is a fairly common species.

Adult Cane ToadChiapas, Mexico

These are massive toads. Adults have exceeded 5 pounds in mass and been over 15 inches long.

The call of the Giant Toad is actually what you would expect for a huge toad. Toads generally have trilled calls. Smaller toads have faster, high-pitched trills and big toads have slower, low-pitched trills. The bigger the toad the lower pitched the trill. The trill of the Giant Toad is so slow and low pitched that it is drum-like. This individual was from north of Aguas Zarcas, Costa Rica.
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Here's a slightly longer section of call from an individual near Caño Negro, Costa Rica.
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Giant Toad call from Caño Negro, Costa RicaAnd here's my only recordings of Texas Giant Toads. This is a chorus of individuals calling from a resaca in Hidalgo County, Texas.
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Giant Toad call from Hidalgo County,
Texas

Stauffer's Treefrog (Scinax staufferi) is a common small frog over much of Eastern Mexico down through central America to northern Costa Rica. They are usually brown in overall all color and may have a pattern of darker brown spots. Like other Scinax, they have rather elongate bodies and a relatively pointed nose.

They call from the grassy edges of ponds and flooded ditches.The call of Stauffer's Treefrog is a short rasping buzz. Here's a recording from east-central Campeche, Mexico.

Looking at the spectrogram for a few calls we can see that the buzzy call is level in pitch and has two major dominant frequencies. We can also see how the two frogs calling here alternate the pitch of their calls to stand out from their neighbors.

The Yucatecan Casque-headed Frog (Triprion petasatus) is a good example of where old sayings sometimes fall short. The old adage goes "if it looks like a duck and sounds like a duck, its a duck". But this is a case where an animal that looks and sounds like a duck....is actually a frog!These strange duck-billed treefrogs is restricted to the Yucatan Peninsula where they are quite common during the rainy season. They can be found on roads and trails at night and their calls can be heard from any wooded area.

Their bizarre head ornamentation ("casque") is actually composed of bony shelves and ridges of the skull which are fused to the cranial skin. They not only have a duck-like beak, but there is a bony ridge coming forward from each eye towards the midline of the skull.

The function of this bony ornamentation is unknown but it has been hypothesized that these frogs use these bony plants to block their burrow entrances during periods of inactivity.

These strange duck-billed treefrogs have an equally strange breeding method. Because they live in the porous karst limestone of the Yucatan platform, there are few areas where water naturally stands on this porous ground. These treefrogs have adapted by laying eggs in any pool of standing water. We found the frog below calling from above a small hollow in a tree, no more than 2 inches in diameter and a few inches deep. He was trying to attract a female to lay eggs in that small temporary pool that had formed in that tree hollow three feet off the ground.

Triprion tadpoles are as strange-looking as their parents. Fairly early in development they get these bony casque structures on their heads and they are visible even in the tadpoles.The problem with nesting in pools in rocks or tree holes is that there isn't much nutrition available for the developing tadpoles. We observed these tadpoles in a water filled depression in a limestone rock. The depression was only a few inches deep and we observed the tadpoles feeding on each other. You can see some tadpoles feeding on another individual in this video towards the end. This tadpole cannibalism is common in other frogs that nest in ephemeral water bodies as well.

Just as you would imagine from a "duck-like" frog, the call is a nasal duck-like quacking. Here's an individual from near the town of Pisté, Yucatan, Mexico.
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And here's a small group, also from south of Pisté, Yucatan, Mexico.
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The two US toad species that are probably confused more than any others would have to be the American and Fowler's Toads (Anaxyrus americanus vs. Anaxyrus fowleri).

The problem is that they overlap in range across much of the eastern/northeastern half of the US and that they occupy much of the same habitats. They are both highly variable in color pattern and there is significant overlap in their characteristics. These two toads are confusing and difficult to tell apart even for experienced herpetologists (people who study reptiles and amphibians).

Fowler's ToadCherokee County, Texas

American ToadScott County, Arkansas

One thing that can be helpful occasionally for distinguishing the two species is that American Toads cansometimes have a reddish ground color. Fowler's Toad is usually gray/brown/black without the reddish tint. However, many American Toads do not have this reddish coloration and some Fowler's do. So if you find one of these two species and it is very reddish, it is probably an American Toad,...maybe. (It should be noted that other toads can be reddish, so not every reddish toad is an American Toad, it is just less likely to be a Fowler's Toad.)

One character that is often quoted in comparisons is the number of tubercles ("warts") in each of the dark spots on the back. If it has only a single (or two) warts in each dark spot, it is probably an American Toad. If it has three or more in some of the spots, it is probably Fowler's Toad.

Another characteristic used to "differentiate" them is the contact between their parotoid glands (big gland behind the eye on most toads) and the bony cranial ridges behind the eye. In American Toad there is a small spur on the cranial crest behind the eye that points posteriorly and touches the front of the parotid gland. You can see the small spur connecting the cranial crest to the parotoid gland in this American Toad from North Carolina.

American ToadNorth Carolina

In Fowler's (and Woodhouse's) Toads, the spur is usually missing and the parotid gland bumps right up against the transverse part of the cranial ridge. There is a nice diagram of this from the Frogs of Tennessee page here -

Another character that is sometimes mentioned is the color of the underside of the toad. American Toad is whitish underneath while Fowler's Toad can have some dark spotting particularly near the throat and front limbs.

Yet another characteristic that is used to distinguish them is the size of the tubercles (warts) on the tibial part of the leg. American Toad has prominent "warts" here while Fowler's are less noticeable and not larger than the rest of the leg tubercles.

So by looking at the tibial warts, cranial crests, parotid glands, belly coloration, and warts-per-spot on the back, you might be able to identify one of these toads to species. But these variables are hard to see in some individuals and apparently vary between species as well!

Now, in Texas the American Toad has a very limited range so the area of possible overlap is fairly small. These two species (and maybe Woodhouse's Toad) would only be expected to occur together in the counties of far NE Texas. The area of overlap is not completely defined as the known range of the American Toad in Texas is rather spotty.

So the experts can sometimes have difficulty telling these species apart, so

1. how do we tell them apart?

and

2. how do we know they are two species?

Well, the answer to both of those questions is their calls. Frog calls serve as reproductive isolating mechanisms. They generally prevent species from interbreeding. A female American Toad is not likely to be attracted to or approach a male Fowler's Toad because their calls sound so different.

Fortunately for us, we can also use these calls differences to identify which species of toad we are dealing with.

Both species have typical toad-like trilling calls. The difference is the length and tone of the calls. Fowler's (and Woodhouse's) Toads have short, buzzy, nasal trills that rarely last more than 3-4 seconds.

American Toads have a similar trill that is "cleaner/prettier" and a little less nasal sounding and often last between 5 and 30 seconds or more.

Here's a spectrogram comparing the two call lengths (American Toad on top, Fowler's on the bottom). You can see the American Toad trill continuing for almost 14 seconds while the Fowler's tapers off within 3 seconds. You can also see that the Fowler's Toad call is "messier" on the Y axis (frequency axis). This tells you the call will be buzzy rather than the clean almost single pitch call of the American Toad.

And here's what that difference sounds like. These 15 second recordings include a single call by an American Toad while the same time period includes three calls of Fowler's Toads. The difference is so obvious that in spite of their physical similarities, you aren't likely to confuse a calling American and Fowler's Toad.

First the long pretty, whistled trill of the American Toad:

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then the short, buzzy, nasal trill of the Fowler's Toad. :

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Next year, I hope to be able to post an American Toad recording from Texas.

The American Toad (Anaxyrus americanus) is a widespread and well-known toad of the northeastern United States.

Here in Texas however it has a much more restricted range. It is only known from a few counties in north-eastern part of the state. It's range in Texas isn't fully understood because it is very difficult to distinguish from the more common Fowler's Toad.

I still haven't seen an American Toad in Texas :-( so these photos and this recording come from nearby Arkansas.

In many areas of the northeastern US, this is a common "yard toad". They are variable in general color ranging from brownish-black to bright reddish. They often have dark spots on their back. There is usually a light mid-dorsal stripe visible and a lighter stripe running from the tympanic membrane (ear) down towards the hind leg. These lighter stripes are sometimes obscured by the ground color.

American ToadFairfield County, Connecticut

American ToadNorth Carolina

Our Texas and nearby populations of American Toad are smaller than the typical American Toads of the Northeastern US and have been identified as belonging to a separate subspecies, the Dwarf American Toad (A. americanus charlesmithi).

Dwarf American ToadOuachita County, Arkansas

They breed in spring into early summer. When they breed successfully, you can often find their distinctive helical strings of black eggs in nearby ponds and streams.

American Toad EggsScott County, Arkansas

The call of the American Toad is a very long, high-pitched trill. It lasts from 5 seconds to over 30 seconds. The Dwarf American Toad subspecies has a slightly higher pitched call than the typical larger northeastern subspecies.

Here is an American Toad from the Ouachita National Forest in Arkansas calling from the middle of a forest road low water crossing.

Rio Grande Leopard Frogs (Lithobates berlandieri) will usually call while floating in shallow water. Their vocal sacs protrude laterally from the sides of their heads. This individual was calling from a flooded riparian area underneath a bridge in McMullen County, Texas.

Here is a recording of a Rio Grande Leopard Frog from Bexar County, Texas. It's call could best be described as a series of "croaking" calls.
The higher pitched clicking heard behind the Leopard Frogs are the calls of Blanchard's Cricket Frog Acris blanchardi

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This spectrogram represents the first three "croaks" of the preceding call.

2016 Addendum -

Like most frog species the sound of the call of the Rio Grande Leopard Frog can change with ambient temperature. At lower temperatures, the tempo of the snoring call slows down and sounds a bit different.
You can hear that by comparing these calls from one of my favorite roadside ponds near Quihi, Texas.

One summer evening in August I stopped by there to record some Rio Grande Leopard Frogs along with other species. Here's what they sounded like in this warm shallow pond at an air temperature of 75°F (and a water temperature probably a bit higher than that) -

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I returned to this pond on a cool winter evening (for south TX that is) after it had rained heavily and was 56°F. The only species calling that night was the Rio Grande Leopard Frog.

Notice how much less "snore-like" it sounds.

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